High-pressure Preparation And Thermoelectric Transport Properties Of Doped Skutterudit

With the development of global technology and industrialization,energy crises occur frequently.To this end,the development of green and sustainable use of renewable resources,while improving the efficiency of energy conversion,has become the focus of continuous attention of governments around the world.Thermoelectric materials can effectively recover low-grade heat energy and realize the functions of heat flow power generation and solid state refrigeration.As a representative thermoelectric material in the medium temperature zone,the natural good electrical properties indicate that it is a potential thermoelectric material.However,due to its high thermal conductivity,it has not been widely used commercially.In this paper,high temperature and high pressure method（HPHT）and vacuum hot pressing method（HP）are used to carry out atomic filling,multi-element replacement and introduction of second phase hetero-composite in cobalt ore,hoping to reduce the thermal conductivity of materials and improve the thermoelectric performance of CoSb₃ on the premise of maintaining excellent electrical properties.The research contents are as follows:1、Pure phase CoSb₃ and Te replacement CoSb₃ thermoelectric materials were prepared by high temperature and high pressure technology.The introduction of Te atoms can effectively optimize the carrier concentration and reduce the thermal conductivity of the lattice.The minimum thermal conductivity of Co₄Sb_11.3Te_0.7synthesized by 2 GPa is 1.48 Wm^-1K^-1 at 700 K,which is 55%lower than that of pure phase CoSb₃.After the successful replacement of Sb atoms by Te atoms with high concentration,a large number of point defects are formed,which can effectively enhance phonon scattering.It can be observed through transmission electron microscope photos that there are a large number of defects and dislocations in the sample,and these microstructure can reduce the thermal conductivity of the lattice,and then reduce the total thermal conductivity.2、Amorphous carbon（C）composite CoSb₃ thermoelectric material was prepared by high pressure method.Amorphous carbon significantly optimized the thermal properties of the sample.The minimum thermal conductivity of CoSb₃+10 wt.%C synthesized at 2 GPa was 0.62 Wm^-1K^-1 at 473 K,which was 83%lower than that of pure phase CoSb₃.In the aspect of thermal parameter optimization,this kind of work provides a new research idea and a certain reference for further exploration of performance optimization.3、Pure phase CoSb₃,multi-walled carbon nanotubes（MWCNTs）composite Te-Ge double displacement CoSb₃ and multi-walled carbon nanotubes（MWCNTS）In filled Te-Ge double displacement CoSb₃ thermoelectric materials were prepared by vacuum hot pressing method combined with nanoengineering.Scanning electron microscopy（SEM）showed that the structure of multi-walled carbon nanotubes,abundant grain boundaries and uniform grain size were clearly observed in the sample.Through high-resolution transmission electron microscopy（TEM）images,it is found that there are a large number of nanocrystals,defects and dislocations in polycrystalline samples,which are conducive to the optimization of thermal properties of materials.The further filling and doping of In atom further reduces the lattice thermal conductivity of the material.At 723 K,the minimum lattice thermal conductivity of In_0.1Co₄Sb_11.2Te_0.5Ge_0.3+0.1wt.%MWCNTs sample is 1.15 Wm^-1K^-1.Compared with the pure phase CoSb₃,The thermal conductivity of the lattice is reduced by about 56%.The results show that the filling composite displacement can effectively reduce the lattice thermal conductivity of the materials,which lays a certain foundation for exploring the high conversion efficiency of CoSb₃-based thermoelectric materials.